Control device for internal combustion engine

Abstract

A control device for controlling an internal combustion engine equipped with an engine body, a variable compression ratio mechanism A configured to be able to change a mechanical compression ratio of the engine body, and an intake system configured to be able to make exhaust discharged from combustion chambers of the engine body be recirculated to an intake passage of the engine body. The control device is provided with a compression ratio control part controlling the variable compression ratio mechanism A so that the mechanical compression ratio becomes the target compression ratio. The compression ratio control part sets the target compression ratio at a lower value when exhaust is being recirculated at a predetermined operating region at an engine low load side than when exhaust is not being recirculated.

The invention claimed is: 
     
       1. A control device for controlling an internal combustion engine, wherein the engine includes:
 an engine body, 
 a variable compression ratio mechanism configured to change a mechanical compression ratio of a cylinder defined within the engine body; and 
 an intake system configured to recirculate the exhaust discharged from a combustion chamber of the cylinder defined within the engine body to an intake passage of the engine body, 
 the control device comprising a compression ratio control part configured to control the variable compression ratio mechanism so that the mechanical compression ratio becomes a target compression ratio resulting in an increase in an actual compression ratio for the cylinder affected by the mechanical compression ratio and an advancement in a timing of a closing of an intake valve configured to introduce intake into the cylinder, wherein the advancement in the timing of the closing of the intake valve closes the intake valve when a piston travelling within the cylinder is further away from a compression top dead center of a compression stroke and increases a temperature of an air-fuel mixture in the combustion chamber at a time of ignition near the compression top dead center of the compression stroke, wherein 
 the compression ratio control part is configured to set the target compression ratio to a lower value when exhaust is being recirculated at a predetermined operating region at an engine low load side than when exhaust is not being recirculated. 
 
     
     
       2. The control device for an internal combustion engine according to  claim 1 , wherein
 the compression ratio control part is configured to set the target compression ratio to a higher value when exhaust is being recirculated at a predetermined operating region at an engine high load side than when exhaust is not being recirculated. 
 
     
     
       3. The control device for an internal combustion engine according to  claim 1 , further comprising:
 an exhaust recirculation control part configured to control the intake system so that an exhaust recirculation rate becomes a target recirculation rate; and 
 an actual recirculation rate estimating part configured to estimate an actual recirculation rate of exhaust, wherein 
 the compression ratio control part is configured to correct the target compression ratio based on the actual recirculation rate until the exhaust gas recirculation rate increases to converge to the target recirculation rate when starting recirculation of exhaust. 
 
     
     
       4. The control device for an internal combustion engine according to  claim 3 , wherein
 the compression ratio control part is configured to: 
 correct the target compression ratio so as to become higher in a predetermined operating region at the engine low load side when the actual recirculation rate is lower than the target recirculation rate; and 
 correct the target compression ratio so as to become lower in a predetermined operating region at the engine high load side when the actual recirculation rate is lower than the target recirculation rate.